1. Field of the Invention
The present invention relates to porous implants and, in particular, to a porous dental implant with improved osseointegration features and that anchor dentures.
2. Description of the Related Art
Conventional dentures have prosthetic teeth shaped and colored to appear like natural teeth. The base of the denture is colored to match gingival or soft tissue, and is fixed upon a patient's gingiva by an adhesive. Oftentimes, however, the denture does not adhere well to the patent's gum causing significant discomfort and malfunction of the denture as well as embarrassment to the patient when the denture slips out of the patient's mouth.
In this case, endosseous implants may be used to anchor the denture to support multiple prosthetic teeth. A denture that fits over implants, or shortened natural teeth if preserved, is called an overdenture.
Endosseous dental implants are typically threaded or press-fit into pre-drilled bores in the mandible or maxilla to support one or more prosthetic teeth. A number of implants spaced along the mandible or maxillae may be used to support a full or partial overdenture. The overdenture is used when the mandible or maxilla of a patient has insufficient bone mass or strength to hold an implant for each tooth, or when such a surgery for so many implants is cost prohibitive or otherwise harmful to the patient. A full denture with prosthetic teeth for an entire upper or lower jaw is usually anchored by two to four implants. The denture may be permanently fixed to the implants or may be removable in a snap-fit arrangement. More stable systems have bars interconnecting adjacent implants and that are covered by an overdenture snapped onto the bars.
However, many years of denture use often result in a reduced alveolar ridge or bone resorption caused by reduced impact from occlusal forces. The localized impact of occlusal forces on the mandible or maxilla is reduced because the denture causes the forces to be impacted by the soft tissue throughout the mandible or maxilla. In this case, further support systems may be needed to hold the denture in a stable position. However, installing even a reduced number of implants for supporting a denture may be too expensive because the alveolar ridge may need to be built up by grafts for example to adequately support a full size implant. Also, grafting procedures often require harvesting bone from other parts of the body or using animal or cadaver bone. The grafting procedure can be painful, the grafts may fail to integrate, and the procedure has some risks such as infection or disease transmission if animal or cadaver bone is used. In other high risk cases such as smokers, diabetics, or osteoporotics that have substantially reduced or missing bone mass, low bone density, and/or abnormally slow bone growth, obtaining adequate support for conventional, full size dental implants may be impossible. Thus, a desire exists to increase the strength of the osseointegration, increase the rate of growth of the osseointegration, and reduce the required size of the dental implant.